The invention relates to a lamp module, particularly for spectral analysis devices, comprising a lamp receptacle body which, for receiving a deuterium lamp having a lamp bulb made of synthetic quartz glass, has a cavity with a beam outlet opening, which is closed with an optical transmission element.
Spectral analysis devices require high optical stability in the sense of a continuous, line-free spectrum in the desired wavelength range. Deuterium lamps are preferred radiation sources for UV spectroscopy, because they emit very intense UV radiation in a range of 180 nm to approximately 400 nm. To cover a broader spectrum, a second lamp—usually a halogen lamp—having a spectrum stretching into the visible range is connected to the deuterium lamp. The spectrum of such a composite lamp module lies in the wavelength range between 180 nm and 1100 nm.
One problem in the use of deuterium lamps is the formation of ozone due to the radiation components of the deuterium plasma below 190 nm. This problem can be solved by selecting a special borosilicate glass, a so-called “UV glass,” which absorbs radiation having a wavelength less than 190 nm for the lamp bulb of the deuterium lamp. The UV glass, however, does not have a steep absorption profile, but instead flattens out toward the long-wave range. Therefore, a portion of the working radiation between 190 nm and 280 nm is still absorbed in lamp bulbs and is therefore not available for spectral analysis purposes.
Another variant of deuterium lamps uses a lamp bulb made of synthetic quartz glass, which is covered completely or partially with a layer acting as an interference or absorption filter for wavelengths below 190 nm. This lamp type is defined as “ozone-free,” because radiation of a wavelength that generates ozone is not emitted from the lamp bulb. However, the direct application of the ozone-suppressing filter layer on the lamp bulb is complicated and offers little clearance room with respect to the further construction of the lamp module.
Deuterium lamps without ozone filters are also on the market in which, for operation in the short-wave spectral range, ozone produced is forcibly removed to the outside or a so-called ozone absorber blocks the ozone before it is discharged into the environment.
From German published patent application DE 39 02 144 A1 a deuterium lamp having a quartz glass bulb is known. The part of the lamp bulb through which the generated radiation is transmitted is covered on its outer side with an ozone-suppressing filter. This involves an interference filter having a layered configuration, wherein the individual layers are applied by vapor deposition in high-vacuum systems. These deposition methods using thin-film technology are expensive and not of unlimited suitability, especially for the production of homogeneous layer structures on curved surfaces. In addition, the thermal loading of these filter layers directly on the surface of the lamp bulb is very high during operation, so that the filter can be damaged already during production and especially during long periods of use of these lamps.
Furthermore, from European patent application publication EP 1 186 828 A1 a deuterium lamp without an ozone filter is known. The lamp bulb is housed in a lamp receptacle body made of aluminum, which is forced air-cooled with an air flow from the rear side by a cooling ventilator. The lamp receptacle body around the lamp bulb is completely closed up to a small opening fitted with a condenser lens for the beam outlet. At the beam outlet window of the lamp housing there is a connecting piece, which leads the radiation outward. The air flow of the ventilator essentially cools or tempers the lamp receptacle body, but does not reach the short-wave radiation in the tubular beam outlet opening, so that no ozone can be generated there and also directly on the lamp bulb. However, because the spectrum of this lamp emitted outward from the beam outlet opening also comprises wavelengths less than 180 nm, ozone formation outside of the lamp module is not prevented.
A similar lamp design is also known from European patent application publication EP 1 201 984 A1. Here, however, in addition to the deuterium lamp, a halogen lamp is also provided, in order to have available a broadened wavelength spectrum for the spectral analysis. Such systems are also called UV-VIS modules, because the spectrum extends into the visible range (VIS=visible).
The deuterium lamp and halogen lamp are arranged one after the other on a common optical axis. The lamp receptacle body of the lamp bulb of the deuterium lamp has in the optical axis a beam inlet opening for the radiation of the halogen lamp arranged behind the deuterium lamp and a common beam outlet opening. Both lamp bulbs could also be housed in the same lamp receptacle body. The cooling by ventilator is here also arranged on the rear side of the lamp housing and does not act on the radiation emitted from the beam outlet opening. Because no ozone filter is provided—also in the lamp according to EP 1 186 828 A1—only the ozone formation within the lamp is suppressed, but not outside of the lamp.